This invention is directed to an improvement in turf units for the provision of natural turf surfaces in environments, such as sports stadia, that are generally unsuited to the continued maintenance and growth of turf. Turfing systems for stadia are known wherein turf plants are grown and maintained in turf units at a location remote from the stadium and, when necessary, transported to the stadium for configuration into a desired playing field. In accordance with such systems, an artificial surface can be transfigured into a natural grass playing surface within a short time period. After use, the turf units may be disassembled and transported back to the growing locations such that the artificial surface of the stadium can be used for other events where a natural grass surface is unnecessary.
One such turfing system is disclosed in the commonly assigned U.S. Pat. No. 5,187,894--Ripley, et al. In the turf units disclosed in Ripley, a growing medium is disposed in growing pans, or trays, wherein substantially entire turf plants are grown and maintained within the growing trays. The level of the top surface of the growing medium, and thus, the level of the turf plants, is maintained at a significant height above the level of the sidewalls of the growing pans. Accordingly, when a plurality of turf units are placed adjacent each other to construct a playing field, a continuous natural grass playing surface is created at a significant height above the level of the growing trays. It is desirable to maintain the level of the playing surface above that of the growing trays so that the trays do not interfere with the participants using the surface. For example, when the natural grass surface is used for a sport such as football where the athletes exert tremendous forces on the turf, the situation must be prevented where the athlete's foot digs into the natural grass playing surface between adjacent turf units such that the athlete's foot comes into contact with the growing trays, perhaps causing injury to the athlete.
In order to provide a playing surface at a significant height above the level of the side walls of the growing trays, the trays are designed such that a barrier, or fence, maintains the growing medium at a level above the top of the sidewalls of the growing trays while the turf units are maintained at the remote growing location. In the patented system discussed above, a removable collar is fitted onto the top edge of the growing pans for maintaining the growing medium at a level above that top edge. When the turf units are assembled together at the stadium, the collars are removed as the turf units are positioned adjacent each other such that the growing medium, along with the turf plants, extending above the top edge of a growing pan contacts the growing medium of the adjacent turf unit.
However, it is known that handling of the collars after they are removed from the growing trays is time consuming since four collar sections are generally used for each tray and a substantial number of trays are used to construct a regular sized athletic field.
Moreover, the growing pans of the above-referenced systems are generally square pans or the like wherein the sidewalls of adjacent pans are abutted against each other when the natural grass surface is constructed. Thus, in these systems the growing medium beneath the playing surface is continuously filled in over the entire area below the playing surface, with the exception of the space taken up by the side walls of the growing pans. Accordingly, these systems require a costly surplus of growing medium and lack space below the playing surface to provide for drainage of excessive water in the event of a rainstorm over an uncovered stadium.